Epitaxial growth process



April 28, 1970 H. M. MANASEVIT ET AL 3,508,962

' EPITAXIAL GROWTH PROCESS Filed Feb. 5, 1966 GAS EXIT

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x a? z 5 INVENTORS HAROLD M. MANASEVIT WILLIAM l. SIMPSON ATTOR NEYUnited States Patent 3,508,962 EPITAXIAL GROWTH PROCESS Harold M.Manasevit, Anaheim, and William I. Simpson,

La Puente, Calif., assignors to North American Rockwell Corporation, acorporation of Delaware Filed Feb. 3, 1966, Ser. No. 524,765 Int. Cl.C23c 11/00 US. Cl. 117227 5 Claims ABSTRACT OF THE DISCLOSURE Theinvention is directed to a process for growing an epitaxial film on asingle crystal substrate comprising the steps of forming initially anextremely thin film of semiconductor material on a desired substrate orsurface by thermal decomposition of a hydride. Subsequently, a thickerfilm is deposited or grown on the thin film by thermally decomposing ahalide in a hydrogen atmosphere or a mixture of halides and hydrides ina hydrogen atmosphere.

This invention relates to a process for improving the quality of asingle crystal films grown on single crystal substrates.

Vapor deposition processes for depositing single crystal films on singlecrystal substrates often produce films of low quality. Defects in thesubstrate surface have a tendency to produce depositions withimperfections. The defects are more noticeable when thicker films areproduced. Twinning in the deposited films also occurs more frequentlywhen using existing deposition processes.

A process is needed whereby certain substrate surface defects can betolerated and thick, high quality films can be produced with a minimumof twinning. Such a process would permit greater latitude in techniquesof crystal growth when forming epitaxial films.

The improved process could also be useful in the formation of compositesuseful in the technology of translating devices, e.g. lasers,transistors, rectifiers, diodes, and other materials and devicesassociated with the field of microelectronics.

Therefore, it is an object of this invention to provide a process forproducing thick, high quality single crystal films on single crystalsubstrates.

Another object of this invention is to produce single crystalline filmson single crystalline substrates with-a minimum of twin densities.

It is still another object of this invention to provide a process forimproving the quality of thick single crystal films on single crystalsubstrates.

It is still a further object of this invention to provide a process forproducing high quality single crystalline films on single crystallinesubstrates having some surface defects.

The invention in a particular embodiment may be characterized as aprocess for growing an epitaxial film on a single crystal substratecomprising the steps of forming initially an extremely thin film ofsemiconductor material on a desired substrate or surface by thepyrolysis (thermal decomposition) of a hydride. This step may be calledthe nucleation step. Subsequently, a thicker film is deposited or grownon the thin film by thermally decomposing a halide in a hydrogenatmosphere or a mixture of halides and hydrides in a hydrogenatmosphere. The materials are decomposed on the thin surface for such aperiod of time as required to produce a desired film thickness.

Each of the process steps has particular merits which when combined,results in producing a thick, high quality semiconducting film on asubstrate.

The first step provides an extremely high density of discretesemiconductor nuclei which tend to agglomerate such that many surfacedefects, for example dirt, fine scratches, small substrate defects, etc.are eventually overcome by the rapidly growing film. Films thusnucleated have displayed twinned densities much less than films formedby halide nucleation. After the nucleation step, the remainder of thefilm is produced by thermal decomposition of materials exemplifiedherein.

These and other objects of the invention will become more apparent inconnection with the following description and figures of which:

The figure is an illustraiton of the apparatus used in depositing thefilms on the substrate.

Referring now to the figure wherein substrate 1 is placed insidevertical reactor 2 on a pedestal 3 which is suspended in an area to 'beheated by coil 4. The coils are activated by an RF source (not shown).The system includes flow meters 5, 6, 7, 8 and 9 including valves 101-1, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 and 33 forcontrolling the flow of material into and out of reactor 2. The systemmay also include deoxidizer 25, molecular sieves 26, and traps of liquidnitrogen 27. Other material sources such as a hydrogen source 28,silicon tetrachloride (SiCl source 29, silane (SiH source 30, germane(Gel-I source 31, diborane (B H in H source 32 are also shown. Some ofthe materials may not be used in every process.

In depositing silicon, halides such as trichlorosilane, silicontetrabromide, and silicon tetraiodide may be used as alternate siliconsources for the second step of the process. Higher hydrides of siliconsuch as Si H may also be considered for use in the nucleation step 1.

In depositing single crystal germanium, germane (GeH and germaniumhydrides followed by germanium tetrahalides or trichloro germane inhydrogen may be used.

Substrate materials such as sapphire, beryllium oxide, magnesium oxide,silicon, germanium, chrysoberyl, calcium fluoride, Group IIV compounds,Group II'-VI compounds, and others may be considered for single crystaldeposits.

In the examples, it has been observed that the thickness of the filmdeposited in the nucleation step should be at least from 500 A. to 1,000A. in thickness, whereas the total film deposited by thermaldecomposition need only be limited by the thickness desired for use in aparticular device. It was also observed in films investigated that thedegree of microtwinning is related to the nucleation step and isrelatively unaffected by the second step.

The invention is further described in the following examples of which:

EXAMPLE I The sapphire substrate was placed on a pedestal inside avertical reactor and heated by radio frequency to a temperature ofapproximately 1150 C. A silicon film was nucleated by 15-30 secondpyrolysis of a 0.3 mole percent silane concentration in hydrogen flowingat about 3 liters per minute over the substrate. After a film having athickness of between 500 and 1,000 A. was deposited, valves 21 and 24were activated to cut off the silane source; and silicon tetrahalide wasintroduced into the hydrogen stream by manipulating valves 10, 11, 12and 33 so that enough hydrogen was diverted through the SiSl, bubblerkept at a temperature of approximately 0 so that about 0.3 mole percentSiCL, passed into the reaction zone containing the substrate. For theconditions used, a silicon growth rate of about 0.3 micron per minuteresulted.

Twin density comparison were made for different samples and orientationsof sapphire substrates when the nucleation step was omitted. In thetable, it is shown that when the nucleation deposit was made usingsilane, the density of microtwins was significantly lower than thecorresponding deposit using SiCL; only. Considering the total amount ofdeposited silicon as 100%, the percentages in the matrix columnrepresent the untwinned material. The remaining material was dividedamong the four possible first order microtwins (T -T with respect to theprimary orientation which can exist in silicon.

TABLE I.RELATIVE X-RAY INTENSITY DATA It should be understood that thesubstrate material does not necessarily have to be identical to thedeposited semiconductor material, for example, germanium on silicon,boron on silicon, silicon on beryllium and other combinations may beused.

We claim:

1. A process for improving the quality of semiconductor epitaxial layersgrown on single crystal substrates EXAMPLE II In a subsequentexperiment, using the same apparatus and same general process steps, twopolished sapphire (alpha-alumina) substrates cut from the same boulewere placed individually in the vertical reactor 2 and heated as before.Two 6.6 micron films of silicon were grown; one by the use of silane andone by the improved two step process. The film formed by the two stepprocess was more uniform in thickness and had the physical appearance ofa better quality film. The two step process film had betterreflectivity, surface structure, etc. as determined by test.

EXAMPLE III In a subsequent example, using silicon as a substrate, theprocess as set forth in Example I was duplicated. The same generalresults were obtained.

EXAMPLE IV In a subsequent example, using germanium as a substrate, andfollowing the same process steps as outlined in Example I, germanium wasdeposited at 900 C. from germane ('GeH and then from germaniumtetrachloride. The same results were obtained as before.

EXAMPLE V In a subsequent example, using boron as a substrate, boron wasformed from diborane (B 111 as the nucleate material followed byadditional boron formation from boron tribromide. The apparatus asdescribed in Example I was used and the same general results wereobtained.

Substrate materials as beryllium oxide, magnesium oxide, silicon,chrysoberyl, calcium fluoride, Group 1IIV compounds, Group II-VIcompounds may also be used as substrate materials under proper substratetemperature conditions.

After the films are produced, semiconductor devices are fabricated inthe films. 'It was determined by measuring characteristics of theproduced semiconductor devices that the devices produced in films formedby the two step process have relatively improved characteristics overthose produced in films from the one step process.

comprising the steps of forming a nucleation film of semiconductormaterial on a single crystal substrate by thermally decomposing a silaneand depositing on said film a relatively thicker layer of silicon bythermally decomposing a silicone halide in a hydrogen atmosphere.

2. The process as recited in claim -1 wherein said substrate is selectedfrom the class consisting of sapphire, beryllium oxide, chrysoberyl andsilicon.

3. A process for improving the quality of semiconductor epitaxial layersgrown on single crystal substrates comprising the steps of forming anucleation film of semiconductor material on a single crystal substrateby thermally decomposing a germane and depositing on said film arelatively thicker layer of germanium by thermally decomposing agermanium halide in a hydrogen atmosphere.

4. The process as recited in claim 3 wherein said substrate is selectedfrom the class consisting of sapphire, beryllium oxide, chrysoberyl,silicon and germanium.

5. A process for improving the quality of epitaxial layers grown onsingle crystal substrates comprising the steps of forming a nucleationfilm of semiconductor material on a single crystal substrate bythermally decomposing a boron hydride and depositing on said film arelatively thicker layer of boron by thermally decomposing a boronhalide in a hydrogen atmosphere.

References Cited UNITED STATES PATENTS 3,312,572 4/1967 Norton et al.3,341,376 9/1967 Spenke et al. 148175 3,160,521 12/1964 Ziegler et al23223.5 X 3,192,072 6/1965 Ziegler et al. 148175 X OTHER REFERENCESPowell et al.: Vapor Plating, 1955, pp. 106-ll1 relied upon.

ANDREW G. GOLIAN, Primary Examiner US. Cl. X.R.

